Non-Patent Literature 1 discloses use cases and potential requirements regarding Long Term Evolution (LTE) based Vehicle-to-Everything (V2X) services. The V2X means vehicular communications and includes Vehicle-to-Vehicle (V2V) communications, Vehicle-to-Infrastructure (V2I) communications, and Vehicle-to-Pedestrian (V2P) communications. The V2V communications or the V2V Services are communication or services between User Equipments (UEs) that are installed in vehicles and use V2V applications. The V2I communications or the V2I Services are communications or services between a UE and a Road Side Unit (RSU), both of which use V2I applications. The V2I communication includes Infrastructures-to-Vehicle (I2V) communications, unless otherwise specified. Further, the term “UE” as used herein includes not only a UE installed in a vehicle but also a UE carried by a pedestrian. The RSU is an entity located on a road side and supports V2I Services including transmission and reception to and from vehicle UEs that use V2I applications. The RSU is installed in a base station, such as a LTE base station (i.e., Evolved Node B (eNB)), or in a stationary UE. The V2P communications or the V2P Services are communications or services between a vehicle UE and a pedestrian UE, both of which use the V2I application. The V2P communications may be performed via an RSU and is, accordingly, referred to as V2I2P communications or P2I2V communications.
Some use cases regarding the V2I Service disclosed in Non-Patent Literature 1 will be introduced here. Non-Patent Literature 1 discloses, in Section 5.6 V2I Emergency Stop Use Case, a configuration in which a vehicle and an RSU are each equipped with a Prose-enabled UEs and the vehicle and the RSU perform Proximity-based services (Prose) communication. ProSe communication is device-to-device (D2D) communication and includes direct communication between two or more ProSe-enabled UEs that are in proximity to each other. In this use case, a vehicle A transmits a message indicating an event, such as an emergency stop, to a service RSU. The service RSU receives this message from the vehicle A and then relays this message to its surrounding vehicles. All vehicles within the transmission range from the service RSU are able to receive this message.
In the use case disclosed in Section 5.14 “V2X Road safety service via infrastructure” of Non-Patent Literature 1, an RSU C detects that an accident has occurred in the area where the RSU C manages. The RSU C indicates the occurrence of this accident to a remote server (e.g., a Traffic Safety Server (TSS) or an Intelligent Transport Systems (ITS) server) and starts transmission of this information in the area. The server informs other RSUs near the RSU C that there is an accident in the area managed by the RSU. The other RSUs start transmission of V2X messages indicating that there is an accident in the area indicated by the RSU C.